Light stable forms of antimonous oxide are used in the manufacture of paints, plastics and ceramic ware, because of the extreme whiteness of the material and its stability against darkening in the presence of light.
Antimonous oxide exists in two crystal states, one is cubic (senarmontite) and the other orthorhombic (valentinite).
While naturally occurring valentinite is light insensitive, valentinite formed by the hydrolysis of solid antimony trichloride in the presence of aqueous ammonia at elevated temperature heretofore results in a product which is light-sensitive and will darken upon exposure to light.
Light sensitivity of synthetically produced valentinite has been attributed to absorbed water and the product has been converted to a light insensitive material when heated under vacuum to a temperature of at least 250.degree. C.